"After the dissuasion by means of whistle-blowing, shouting and hand-flag guiding was of no avail, the Chinese naval vessels fired two red signal shells into the sky as a warning, and the signal shells burned out and extinguished in the air," Xinhua quoted the official as saying.

"There is no such things that Chinese vessels fired with weapons or the Vietnamese fishing boats caught fire."

China says the Vietnamese boats were illegally fishing in what it says is its territory when the incident occurred on 20 March.

Vietnam has lodged a formal complaint with the Chinese embassy in Hanoi, with its foreign ministry calling the incident "very serious".

'Patrol missions'
Meanwhile Chinese state media also reported that the country's navy has visited the southern-most shoal it claims in the South China Sea.

Four ships reached James Shoal - located south of the Spratly islands around 80km (50 miles) from Malaysia's Sarawak - as part of what Xinhua said was a "patrol mission" in the disputed Spratly islands.

The Chinese navy "are determined to safeguard the country's sovereignty with their services on the South China Sea", said Xinhua.

The ships, which left Hainan province on 19 March, "conducted patrol and training missions" over eight days, it added.

In recent years tensions over over-lapping territorial claims in the South China Sea have been rising, amid a more assertive stance from China.

China claims a U-shaped swathe of the sea that extends well into what UNCLOS (UN Convention on the Law of the Sea) recognises as the 200-mile-from-shore Exclusive Economic Zones of other claimants.

Last year, the Philippines and China engaged in a lengthy stand-off over another disputed area, the Scarborough shoal, in a spat that left diplomatic ties very strained.